In sound systems, an equalizer is used to boost or cut certain frequency components in a signal to provide a desired sound from the sound system. Such sound effects may be bringing out a particular instrument's sound or providing a more realistic sound. Two common types of equalizers for sound systems are graphic equalizers and parametric equalizers.
FIG. 1 is a schematic view of a graphic equalizer system 100. A graphic equalizer system 100 comprises a plurality of bandpass filters 120, 124, 128 connected in parallel. Each bandpass filter allows a component of a signal within a bandpass filter frequency range to pass through the bandpass filter. Each component is then amplified by amplifier 130 associated with the bandpass filter. The components are then added together by adders 132. Often a slider board is used to set the amplifiers associated to the bandpass filters. FIG. 2 is a schematic view of a slider board 200 for a graphic equalizer. The slider board 200 has a plurality of sliders 204, where each slider controls an amplifier 130. Often the sliders 204 may be placed in a curved configuration as shown in FIG. 2 to provide a curved equalization, where the middle frequencies are amplified more than the outer frequencies. The sliders 204 may be placed in other configurations to provide other equalizer configurations.
Parametric equalizers are equalizers which may provide more flexibility than a graphic equalizer. A single parametric equalizer allows not only the setting of boost or cut, but also the center frequency and the bandwidth. An example of a parametric equalizer is the TAS3001C Stereo Audio Digital Equalizer chip set by Texas Instruments™. The TAS3001C may provide six parametric equalizer filters. The filters may be placed serially. The parametric equation for each filter may be:
      H    ⁡          (      z      )        =                    b        0            +                        b          1                ⁢                  z                      -            1                              +                        b          2                ⁢                  z                      -            2                                      1      +                        a          1                ⁢                  z                      -            1                              +                        a          2                ⁢                  z                      -            2                              Five coefficients b0, b1, b2, a1, and a2 may be provided to the parametric equation to define the center frequency and bandwidth of the filter. The coefficients may be provided in a format providing 4 bits for an integer part of the coefficient and 20 bits for a fractional part of the coefficients. One method of providing center frequencies and bandwidths to the filters is by placing numbers in a spreadsheet. The coefficients would be derived from the numbers in the spreadsheet and sent to the filters. From the resulting sound, a new set of numbers may be submitted. Through trial and error, a preferred set of center frequencies and bandwidths may be found.
It would be desirable to provide an improved interface for an equalizer.